As capacitors having a large capacitance and a low ESR (Equivalent Series Resistance) used in various electronic devices, aluminum solid electrolytic capacitors or tantalum solid electrolytic capacitors have been used.
A solid electrolytic capacitor is constituted by a primary electrode (conductor) made of an aluminum foil having micropores in its surface layer or of a sintered body of tantalum powder having fine pores in its inside, a dielectric layer formed on the surface layer of the electrode (having fine pores), and a secondary electrode (usually, a semiconductor layer) formed on the dielectric layer on which a conductor layer is formed. Generally, a lead wire is taken out from the primary electrode, and a terminal is connected to the lead wire and the conductor layer formed on the secondary electrode. To this lead wire and to the second conductive layer, terminals are connected respectively.
Conventionally, in mass production of such capacitors on industrial scale, two or more conductors as described above (such as aluminum foil and sintered body of tantalum powder) are soldered or welded to a metal long plate at even intervals and then this plate is subjected to treatments of forming dielectric body and semiconductors (Patent Document 1: Japanese Patent Application Laid-Open No. S60-249310).
Specifically, as shown in FIG. 1, lead wires 2 are taken out from conductors 1 for producing capacitors. The end of each of the lead wires is fixed with solder 4 onto a metal long plate 3 at even intervals. Thus, a member 5 for producing capacitors from which a plurality of conductors 1 hang down is prepared. Next, the conductors are immersed in a separately-prepared container containing a solution for chemical formation and by using the long plate as anode and an electrode present in the solution as cathode, electric current is passed, to thereby form a dielectric layer. Further, the conductors are immersed in a container containing a raw material for forming a semiconductor layer and in a container containing a solution for oxidizing the material to form a semiconductor alternately. Or, the conductors are immersed in a container containing a raw material for forming a semiconductor layer and by using an external electrode provided in the vicinity of conductors as anode and an electrode present in the contained as cathode, electric current is passed to thereby electrochemically laminate a semiconductor layer on the dielectric layer.
However, a semiconductor layer chemically formed by conventional method is, as compared with one formed by electrochemical method, has uneven in its thickness or the composition or continuity of the semiconductor layer itself is not constant (For example, in a case where the semiconductor layer is an electroconductive polymer, the polymer includes branches.) For these reasons, the semiconductor layer has a high resistivity and as a result, a capacitor thus produced has a disadvantage of a large ESR (Equivalent Series Resistance). Moreover, in carrying out each step for electrochemical treatment, it is difficult to always provide an external electrode in the vicinity of each conductor at even intervals. That is, due to variation in locations of external electrodes, current values passed to the conductors cannot be uniform, rendering formation of semiconductor layers of thus produced capacitors not uniform and therefore, it has been difficult to produce capacitors having stable capacitance. This problem is irrelevant in production process which includes several or less conductors. However, it can be a major problem in production process which includes formation of semiconductor layers on industrial scale, for example, on several hundred of conductors at a time.
Furthermore, in a case where a metal long plate is used as anode in electrochemical formation of semiconductor layer, if a large amount of current is passed to one conductor (for example, to the leftmost conductor in FIG. 1), the current amount to be passed to the other conductors may become insufficient. For this disadvantage, forming uniform semiconductor layers have been sometimes difficult in some cases.
The present inventors have proposed a jig for producing capacitors which enables industrial-scale production process of solid electrolytic capacitors having narrow variation in capacitance, in which process formation of semiconductors layers is stable in case of electrochemically forming dielectric layers and a conductor layers on a plurality of conductors sequentially. However, the long plate the jig for producing capacitors uses is not a mere metal plate but a circuit board having constant current source. For example, if conductors (lead wires of conductors) were soldered onto this circuit board and the board were disposed after each production process, it would increase production costs. On the other hand, in order for the production jig to be repeatedly used in production, it can be considered, for example, to remove soldering and wash the board to clean the surface every time when one production process is completed. However, this approach is not advantageous on cost front. Further, in order for each of product capacitor elements to be taken out from the production jig, it is necessary to heat soldered portion to thereby remelt the soldering or to stress the soldered portion to thereby peel off the element together with soldering from the plate. However, such a process sometimes results in removal of soldering attached onto the end of the lead wire of the product capacitor element.    [Patent Document 1]    Japanese Patent Application Laid-Open No. S60-249310